Is there a way in Python to check whether an entry to os.environ is a variable or a shell function?

Question

With the os module in Python we can easily access environment variables through the dict os.environ. However, I found out that os.environ does not just hold variables, but also globally defined shell functions (e.g. from the module software package).

Is it possible from within Python to find out whether a given entry in os.environ actually is a function and not a variable? Please note that a shell-agnostic solution is preferred, but I could settle for a Bash-specific solution as well.

Answer 1

This feature is bash-specific, so a test for an exported shell function needs to do what Bash does. Experimentation and source code show that Bash recognizes an environment variable as a shell function at startup by the presence of a () { prefix in its value — if the prefix is missing, or even slightly altered, the variable is treated as an ordinary data variable.

Therefore, the equivalent Python check would look like this:

def is_env_shell_func(name):
    return os.environ[name].startswith('() {')

Answer 2

One solution that I find to work (but that is ridiculously clumsy) is the following:

import subprocess

var = 'my_variable_name_i_want_to_check'
p = subprocess.Popen('declare -f ' + var, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
p.communicate()

if p.returncode == 0:
    print('function')
else:
    print('variable')